The tubercle of a rib is an eminence on the posterior surface, at the junction of the neck and body of the rib, and nearer the lower than the upper border. It consists of an articular and a non-articular portion. The articular portion, the lower and more medial of the two, presents a small, oval surface for articulation with the end of the transverse process of the lower of the two vertebrae to which the head is connected. The non-articular portion is a rough elevation, and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper than in the lower ribs[WP]. [ http://en.wikipedia.org/wiki/Tubercle_(rib) ]